SH-EXPR(1) SH-EXPR(1) NAME expr, ntest, mpexpr - shell module for simple arithmetic. SYNOPSIS load expr OR load mpexpr ${expr [ -r radix ] [ arg... ] } ntest num DESCRIPTION Expr and mpexpr are loadable modules for sh(1) that provide support for integer arithmetic. Expr uses 64-bit signed integers; mpexpr uses arbitrary-precision signed integers. They each provide the same interface: a command ntest, which performs a simple boolean test on its integer argument, and the substitution operator expr, which takes an expression in Reverse Polish notation, and yields its result. Ntest returns true if its argument num is non-zero, and false otherwise. Expr evaluates each arg in turn; if it is an integer it gets pushed onto the stack; otherwise it should name one of the operators below, whereupon the appropriate number of operands are popped off the stack, evaluated as arguments to the operator, and the result pushed back onto the stack. Arguments are passed to the operator first-pushed first, so, for instance, ${expr 2 1 -} yields 1, not -1. Alternative names are given for some operators; this is to avoid the necessity of quoting operators that contain sh(1) metachar- acters. Integers are given in the same form acceptable to Limbo. The relational operators yield either 1 (true) or 0 (false). If the -r option is given, radix specifies an out- put base for printed numbers. It may be from 2 to 36; mpexpr also allows 64 to specify base64 notation. Numbers are printed in a form suitable for re-interpretation by expr. When all its arguments have been evaluated, expr yields all the values remaining on its stack, first pushed first. Note that bitwise operators treat their operands as if they were stored in two's complement form. The operators supported by expr are as follows (the number of operands required in is given parentheses). + (2) Addition - (2) Subtraction x, * (2) Multiplication Page 1 Plan 9 (printed 11/27/21) SH-EXPR(1) SH-EXPR(1) / (2) Division. Division by zero raises a divide by zero exception. % (2) Modulus. A zero modulus will cause a divide by zero exception to be raised. and (2) Bitwise-and. or (2) Bitwise-or. xor (2) Bitwise-xor. ~ (1) Bitwise-complement.. _ (1) Unary minus. <<, shl (2) Shift left. >>, shr (2) Shift right. =, ==, eq (2) Equality. !=, neq (2) Inequality. >, gt (2) Greater than. <, lt (2) Less than. <=, le (2) Less than or equal to. >=, ge (2) Greater than or equal to. !, not (1) Logical negation. rep (n) Rep repeats the last operation (which must have been a two-operand operation other than seq) until the values in the stack are exhausted. seq (2) Seq pushes on the stack a sequence of numbers ranging numerically from its first argument up to and including its second argument. If its second argument is less than its first, the sequence will descend. rand (1) (mpexpr only). Push a secure random number; the argument value gives the size of the num- ber, in bits. bits (1) (mpexpr only). Push the size, in bits, of the argument. Page 2 Plan 9 (printed 11/27/21) SH-EXPR(1) SH-EXPR(1) expmod, invert (2) (mpexpr only). See keyring-ipint(2). exp, xx, ** (mpexpr only). Exponentiation. SOURCE /appl/cmd/sh/expr.b SEE ALSO sh(1), sh-std(1), sh-tk(1), keyring-ipint(2) BUGS Postfix notation can be confusing. Any operators that con- tain shell metacharacters (e.g. ``*'', ``>'') must be quoted to avoid interpretation by the shell. Base64 notation can contain # characters, which need quoting to avoid interpre- tation by the shell. Page 3 Plan 9 (printed 11/27/21)